This invention relates to a droplet generator for a continuous stream ink jet print head.
More particularly the invention relates to such a generator comprising: an elongate cavity for containing the ink; nozzle orifices in a wall of said cavity for passing ink from the cavity to form-jets, said nozzle orifices extending along the length of said cavity; and actuator means for vibrating the ink in said cavity such that each said jet breaks up into ink droplets at the same predetermined distance from said wall of the cavity, said actuator means being disposed on the opposite side of said cavity to said wall and comprising vibration means which is divided up along the length of said cavity at least partially into at least two parts. An example of such a generator is disclosed in U.S. Pat. No. 4,587,528. In order that each jet breaks up at the same distance from the generator, it is necessary that the vibration of the actuator means has no component along the length of the ink cavity. The at least partial division of the vibration means of the actuator means inhibits such components.
According to the present invention there is provided a droplet generator for a continuous stream ink jet print head comprising: an elongate cavity for containing the ink; nozzle orifices in a wall of said cavity for passing ink from the cavity to form jets, said nozzle orifices extending along the length of said cavity; and actuator means for vibrating the ink in said cavity such that each said jet breaks up into ink droplets at the same predetermined distance from said wall of the cavity, said actuator means being disposed on the opposite side of said cavity to said wall and comprising vibration means which is divided up along the length of said cavity at least partially into at least two parts, characterised in that said actuator means further comprises a backing member disposed further from said cavity than said vibration means and secured to and bridging said parts into which said vibration means is at least partially divided, said vibration means being interposed in line between said backing member and said cavity.
Preferably, said actuator means further comprises a head on the opposite side of said vibration means to said backing member and secured to and bridging said parts into which said vibration means is at least partially divided.
Preferably, said vibration means is divided up along the length of said cavity into at least two spaced parts. Suitably, the number of spaced parts is three.
Preferably, said vibration means is made of piezoelectric material.
Preferably, the backing member and, when provided, the head are made of an electrically conductive material. Suitably, the electrically conductive material is brass for the backing member, and steel for the head.